In Martinis' recent Caltech lecture on the Sycamore paper, he appears to make much of the fact that FIG. 4 of the paper show straight-line fidelity - that is, the fidelity decreases log-linearly with an increase in the number of qubits, and an increase in the depth (number of gates) of the circuit.
I believe a position of Martinis is that the scientific value of Sycamore, which is independent of the claims of supremacy, is that errors can be modeled collectively as digital Pauli errors, and further these errors are independently distributed and don't cluster. This seems to conflict with, for example, Kalai's objection to quantum computing that errors collude and coordinate with increasing qubit count/depth.
Martinis notes that "high school probability" can be used to model the decrease in fidelity with an increase in qubit count/gate count.
But what is this "high school probability" that Martinis refers to?
If I were to model insertion of errors into a large-depth circuit, I might decide, with probability $p$, to insert a randomly selected Pauli error (bit-flip and/or phase shift) between any two gates. The probability would be independent of the depth/qubit count of the circuit.
Is this "Poisson-process" of error-insertion similar to the high school probability to which Martinis refers?